The present invention relates generally to methods for controlling machine tools or robots, and more particularly to a method for controlling the acceleration and velocity (i.e. the feedrate) of at least one controllable axis of a machine tool or robot.
In certain machining processes, which are performed with numerically controlled machine tools or robots, a so-called pendulum or oscillating motion is superimposed on a movement along a trajectory. From robotics, two different solutions for generating this pendulum motion are known. They can be described by the terms "cartesian" and "axis-specific" oscillation, i.e. swinging in pendulum fashion. In the case of "cartesian" oscillation, the cartesian coordinates of the pendulum figure or pendulum curve are specified and transformed by the robot control into a robot-specific coordinate system. It is not a question in this case of actually superimposing a pendulum motion on any path at all, but rather of producing the actual path right from the start in the form of a pendulum motion. Since this method requires a control setpoint selection for all robot axes, it entails a large computing capacity and considerable time.
The axis-specific pendulum movement pertains to an actual superimposition of a pendulum motion on to any movement along a trajectory. The movement along a trajectory is calculated by the numerical control for all axes of a machine tool or a robot, and the pendulum motion is carried out each time from the last axis, that is usually the tool-bearing axis.
One advantage of the "axis-specific" pendulum movement is that a time-consuming conversion of the cartesian pendulum values into axis-specific values, as is required in the case of cartesian pendulum movement, need not be performed. Thus, higher pendulum frequencies can be reached with axis-specific pendulum movement than with cartesian pendulum movement, so that axis-specific pendulum movement still remains relevant technology.
When previous axis-specific pendulum methods are applied, the acceleration and deceleration ramp calculation for generating the motion of the pendulum axis is carried out in the fine interpolator. For that reason, on the one hand, the time needed to calculate the pendulum motion is still relatively long and, on the other hand, the acceleration and the pendulum velocity must be constantly monitored, so that permissible limiting values are not exceeded.
Another disadvantage of the axis-specific pendulum method lies in the fact that a change in the tool path feedrate cannot be taken into consideration by the pendulum motion, which change is supposedly able to be initiated by the user by stipulating an override value, for example, or can be automatically initiated by means of sensors. This is because the calculations with respect to a change in the tool path feedrate are already carried out in the cartesian interpolator, which is connected to the fine interpolator. An override setpoint selection, through which means the tool path feedrate is decelerated, for example, would cause the pendulum figure to become distorted, since the velocity of the pendulum movement does not change with the tool path feed rate.
The present invention is directed to the problem of developing a method for controlling the acceleration and velocity of at least one numerically controllable axis of a machine tool or robot, with which the above-mentioned disadvantages are avoided.